Pothead termination comprising a vapor condenser and a tubular conductor extension containing a vaporizable liquid, and method

ABSTRACT

A pothead for a high voltage cable, which may be of the type with a central pilot wire for monitoring the temperature of the cable conductor, comprises an electrically conducting tubular member compressed onto the cable conductor, a liquid condenser mounted outside the pothead insulator and a volatile liquid within the tubular member. The condenser may have radial fins in proximity to a corona ring and be surmounted by a temperature monitor and radio transmitter.

United States Patent 1 1 E'ngelhardt 1 Oct. 23, 1973 [54] POTHEADTERMINATION COMPRISING A 2,748,184 5/1956 Nicholas 174/19 VAPORCONDENSER AND A TUBULAR g; g g 'Z f a er CONDUCTOR EXTENSION CONTAININGA 3,662,137 5/1972 Cleaveland 174/15 an ux VAPORIZABLE LIQUID, ANDMETHOD Inventor: John S. Engelhardt, Hartsdale,

Assignee: Anaconda Company, New York,

Filed: June 7, 1972 Appl. No.: 260,626

US. Cl 174/11 BH, 29/592, 174/15 BH, 174/19 Int. CL... H02g 15/22, H02g15/28, H02g l/14 Field of Search 174/11 R, 11 BH, 174/12 BH,14 BH, l5BH, l6 BH, l8, 19, 31 R; 29/592, 630 R References Cited UNITED STATESPATENTS 2/1915 Fortescue 174/15 BH X Primary Examiner-Laramie E. AskinAttorneyVictor F. Volk ABSTRACT 14 Claims, 2 Drawing Figures TEMPERATUREMONITORING RADIO TRANSMITTING UNIT 1 PAIENIEI] IIIII 2 3 I875 3.767.835SHEET 10F 2 TEMPERATURE MONITORING AND RADIO TRANSMITTING UNIT CORONARING FIG. I

I I I I II IQJI VAPORIZABLE LIQUID POTI'IEAD TERMINATION COMPRISING AVAPOR CONDENSER AND A TUBULAR CONDUCTOR EXTENSION CONTAINING AVAPORIZABLE LIQUID, AND METHOD BACKGROUND OF THE INVENTION A highvoltage cable invariably Comprises at least one elongated conductingelement, generally of metal, maintained athigh potential when the cableis energized, a wall of insulation surrounding the conducting element,and a grounded sheath or conduit surrounding the wall of insulation.When the cable is terminated, if it were simply cut through, currentwould form an arc across the cut end of the insulation, from theconductor to the sheath. A cable is therefore generally terminated in apothead which provides a high resistance path usually of porcelain,between the exposed conductor, or extension thereof, and the cablesheath. An essential element of a pothead is a porcelain or otherdielectric container into which the cable, minus its sheath, isinserted. Because the sheath, proper, which may typically take the formof a lead extrusion or steel pipe, may be irregularly spaced from thewall of insulation, a grounded electrical shielding, which usuallyincludes a semiconducting underlayer, is applied directly to the topsurface of the cable insulation. Where this shielding wall isterminated, it is well known to be necessary to apply a so called stressrelief cone which has the effect of increasing the thickness of theinsulating wall and reducing the unit electrical stress at the sectionwhere the shielding is discontinued. The termination of the shielding onthe surface of the stress relief cone should be situated within thepothead. The stress relief cone and the walls of the pothead provideelectrical insulation butsin so doing they also provide thermalinsulation with the result that the portion of the cable that isenclosed in the pothead will become hotter than the remainder of thecable and any insulation failure will be most likely to occur there.

Modern potheads for high-voltage cables involve large and expensivestructures weighing a ton or more and having procelain insulators 20 ormore inches in diameter with lengths over feet. They may include costlyappurtenances such as temperature monitors and even radio transmittersas described in Engelhardt et al. US. Pat. Nos. 3,491,597 and 3,633,191.These complexities add, not only to the cost of any pothead failure, butto the difficulty of providing adequate coolmg.

When a cable termination is made with a large pothead, such as a potheadfor 230,000 volt service, the cable sheath is mechanically andelectrically fixed to a heavy base plate having a central openingthrough which the core of the cable including the conductor, insulation,and shielding are caused to protrude upwardly. Customary preparation ofthe protruding core is then performed including exposure of an end ofthe conductor, trimming of the shielding and building the stress reliefcone. After the core has been prepared, the pothead, which willsubsequently be filled with dielectric fluid, is lowered over it by acrane or hoist and fastened to the base plate. No special provision ismade in this customary procedure for removing the heat generated by thevconductor within the pothead.

SUMMARY I have invented a high-voltage cable pothead provided with meansfor cooling the interior of the pothead.

My novel cooled pothead is markedly economical in that it employsstandard insulators and other pothead elements that are commerciallyavailable. My novel pothead achieves a cooling effect withoutsubstantially modifying the desirable electrical field of thetermination.

My high voltage cable pothead which comprises an insulator and is usedwith a cable comprising a conductor and a thick wall of insulationsurrounding the conductor, comprises entrance means into the pothead forthe cable including its wall of insulation and an electricallyconducting tubular member positioned to extend upwardly within thepothead and is at least partially filled with a liquid that isvaporizable at the operating temperature of the pothead. This member ismechanically and electrically joined to the conductor within the potheadwhich also comprises condensing means for the liquid exterior to theinsulator and communicating with the tubular member. The tubular memberpreferably comprises within it a downwardly extending length of tubingfor condensate from the liquid. Preferably my condensing means comprisesradial fins and a corona ring adjacent to the fins having an outerradius at least equal to the radial extension of the fins. The joiningmeans may advantageously comprise a sleeve extending from the tubularmember and compressed over the conductor, and, when my pothead is usedwith a cable comprising a temperature monitoring means, such as a pilotwire, the sleeve may comprise a wall defining an opening leading to thismeans, the tubular member comprises an external lengthwise groove forthe pilot wire with the pilot wire being positioned in the groove, andthe pothead may comprise temperature monitoring means and a radiotransmitter preferably mounted above the condensing means. Preferably mypothead comprises wrappings forming a continuous wall of electricalinsulation over the conductor and the tubular member within theinsulator and preferably also a stress relief cone extending upwardlyover the cable, the joining means and at least a portion of the tubularmember containing the vaporizable liquid.

In my method of terminating a high-voltage cable I expose a substantiallength of the core of the cable ineluding-insulation shielding, beyondthe sheath, remove sufficient of the insulation to expose a length ofthe end of the conductor and mechanically and electrically connect anelectrically conducting tubular member to the conductor end. I wrapinsulation such preferably as a wide sheet of oil-impregnated paper,around the member to the diameter of the insulation on the cable, andbuild a stress relief cone extending from the shielding over the coreand preferably at least a portion of the tubular member. I then positiona pothead over the tubular member and the exposed core, fit a vaporcondenser, communicating with the tubular member, to the pothead, atleast partially fill the tubular member with a liquid, vaporizable atthe operating temperature of the pothead, fill the pothead withdielectric fluid and seal it.

BRIEF DESCRIPTION OF THE DRAWING FIGS. 1 and 2 show a section of apothead of my invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT The pothead indicatedgenerally by the numeral is here applied to the termination of a knowntype of oil-filled pipe-type cable 11 characterized by the fact that thecable sheath consists of a steel pipe within which the cable core 13having a stranded metal conductor 14 surrounded by oil saturated papertape insulation 16 and protected by skid wires 17 has been pulled. Thecable pipe may comprise steel for threeconductor cable but when thesingle phases are divided to enter the pothead they are customarilybrought into branch joints terminating in short non-magnetic pipes 12,preferably of stainless steel or aluminum. The pipe 12 and skid wires 17are terminated at a composite base plate 18 having a central opening 19through which the remainder of the cable core 13 covered by insulationshielding tapes 21 extends upwardly into a porcelain insulator 22supported on a bell cap 23 topping a metal bell 24 and firmly fixed tobronze cementing flanges 26, 27, the former of which is bolted to thecap 23 and the latter to a metal top plate 28. An oilimpregnatedelectrical condenser 29 of usual construction lines the insulator 22; Sofar I have described elements of a conventional pothead such as may beused for a 230 kv oil-filled cable. A novel feature, however, comprisesa tubular copper member 31 with a solid section 32 that extendsdownwardly in a compression sleeve 33 that is solidly crimped onto theconductor 14. The member 31 can also'be made from an open length ofcopper tube by inserting and silver soldering the section 32 attached tothe sleeve 33. Other means of fabricating the member 31 will be apparentto persons skilled in metal fabrication/The member 31 is filled up to apoint 34 with a vaporizable liquid 36. A fluorocarbon with a vaporpressure of 200 pounds per square inch at 65C is suitable for the liquid36 and such a liquid is commercially available under the trademark Freonfrom E. I. du Pont de Nemours and Co. The prec'isevapor-pressurecharacteristics of the liquid 36 are notcritical, however, and may bevaried with the temperature operating characteristics of the cable andthe pressure that can be retained in the pothead. It is only necessarythat a liquid be selected that will reflux when the pothead is inoperation, as shall be explained. The member 31 has been constructed insections silver soldered together with an upper section 37 of reduceddiameter in its lower portion fitted onto a shoulder 38 of a lowersection 39. The diameter of the section 37 can thus be made to fitthrough a standard pothead top plate but building the member 31 insections also permits introduction of a copper funnel-like elementhaving a conical flange 41 and long tubing extension 42 for the returnof liquid condensate near the bottom of the member 31. Perforations43 inthe flange 41 allow vapors from the liquid 36 to pass upwardly to avapor condenser 44 having radial fins 46 mounted above the insulator 22and plate 28. The section 37 passes through the condenser 44 and has asolid portion forming the pothead stem 47 to which high voltageelectrical connection is made by a clamp 48. Slotted perforations 49within the condenser 44 provide communication between the member 31 andthe condenser 44. By means of the tubing 42 the coolest liquid isreturned close to the conductor 14 and convection occurs within theliquid 36 in addition to vaporization, adding to the efficiency ofcooling. At a point 51 within the bell 24 of the pothead a stress reliefcone 52 is initiated that is built up to its maximum diameter at'a point53 andthence extends to a point 54 more than half way through theinsulator 22. The outer surface of this cone is made conducting in theusual way by the application of copper mesh tape 50 electricallycontinuous with the shielding 21 to a point'55. The member 31 must becapable of carrying the current in the conductor 14since it has replacedthe length of the conductor which would extend through a conventionalpothead. The cable insulation 16 has been tapered in a cone 56 to exposethe conductor to receive the sleeve 33. Wrappings 57, 58 of insulatingquality of oil-impregnated paper sheet have been applied over the member31 to a diameter equal to the diameter of the cable insulation beforestarting the cone 56 and the spaces between paper wrappings have beenfilled in with wrappings 59, 61 of oil-impregnated crepe paper. Thestress relief cone 52 which is also built up of paper wrappings has beenapplied over the in'sulations 16, 56, 59, 57, 61, 58, and heat passingradially through the pothead from the cable would, prior to myinvention, be required to pass through both the insulation and stresscone wrappings, the condenser 29 and insulator 22. At the end 54 of thestress relief cone I have mounted a conventional insulating washer 62and insulating cylinder 63, a similar but longer cylinder 64 lines thecondenser 29 and the latter issurmounted, in the usual way, with aninsulating washer 66 and cylinder 67. Pipe connections 68 to the bell 24and 69 to the plate 28 permit the introductionof dielectric fluid 70which saturates the wrappings and fills all voids. The insulator of thecable 11 and insulating wrappings of the pothead 10 are paper but it isknown to use plastics for insulating highvoltage cables andterminations, and plastic film or paper-such as, for example,polyolefin, polycarbonate, polyphenylene oxide may be used instead ofcellulosic paper within the scope of the present invention.

The fins 46 provide possible points for corona dis charge since thecondenser 44 assumes the electrical potential of the conductor 14 and Ihave provided a smooth surfaced corona ring 71 adjacent to the top ofthe fins 46 to prevent such discharge. The radius of this ring is atleast as large as the radial spread of the fins. The flange 27 which hasa smooth, rounded surface also functions as a corona ring. In theabsence of the flange 27 I recommend that an additional corona ring bepositioned beneath the fins 46.

These corona rings may be omitted where the electrostatic field strengthis not excessive, for example, at voltages below 161 Kv, or when theelectrostatic field is controlled by other means, such as a properlydesigned temperature monitoring equipment housing or externalcontrolling surfaces required by the connecting bus work, such as iscommon in EHV substation design.

The temperature of the conductor 14 is monitored by an insulated pilotwire 72 through its center and I have provided a hole 73 in the sleeve33 and a vertical groove 74 in the member 31 so that this wire can beextended out of the pothead proper to a monitoring and radiotransmitting unit 76 mounted upon the condenser 44. A bushing 77provides for the wire 72 to pass through the plate 28. These featurescan, of course, be omitted where my potheadis used for a cable withoutpilot wire monitoring.

In terminating a cable with my pothead I have found the following methodto be most advantageous. In a pipe type cable the pipe 12 is terminatedat the plate 18 and the cable core pulled through it to expose asufficient length for the connection. In a lead-sheathed cable thesheath is cut off for the same distance and the cut end connected to theplate. The skid wire (in pipe type cable) is cut back to the plate, theshielding trimmed and the insulation pencilled to expose a short lengthof the conductor for connecting to the member 31. The member 31,including the sleeve 33, sections 37, 39, 47, flange 41 and tubing 42which will have been preassembled and silver soldered is then compressedonto the conductor 14 by means of a power tool after first threading thewire 72 through the hole 73. The wrappings 57, 58, 59, 61 are appliedand the stress relief cone with the wire 72 fitted in the groove 74. Thebell 24 with the bell cap 23 is lifted over the member 31 and bolted tothe plate 18. The insulator 22 to which the flanges 26, 27 have beenpreviously cemented is lowered by a hoist over the member 31 and boltedto the bell cap 23. The section 37 is circumferentially grooved at 78,79, 81, 82, 83 for O-rings 84, 85, 86, 87, 88 which can be preapplied.The plate 28 is positioned, bringing the pilot wire 72 through theopening for the bushing 77 and bolted in place. The condenser 44 has acentral opening 91 which permits it to be lowered over the member 31,and thick upper and lower plates 92, 93 that seal respectively againstthe O-rings 85, 86 and 87, 88. The condenser 44, with the corona ring 71fixed to it is then mounted and locked with clamps. The liquid 36 isfilled into the member 31 at any time before the cable is used bypouring it into the condenser 44 through a sealable opening, not shown.The pothead is filled with dielectric fluid through the pipe 68, ventingthrough the pipe connection 69. The monitoring and transmitting unit 76is mounted upon the condenser 44 and connected electrically to the wire72 at the bushing 77.

I have invented a new pothead and method of which the foregoingdescription has been exemplary rather than definitive and for which Idesire an award of Letters Patent as defined in the following claims.

I claim:

I. A pothead, comprising an insulator, for a highvoltage cable, saidcable comprising a conductor and a thick wall of insulation surroundingsaid conductor, comprising:

A. entrance means into said pothead for said cable having said wall ofinsulation,

B. an electrically conducting tubular member positioned to extendupwardly within said pothead,

C. a liquid vaporizable at the operating temperature of said pothead atleast partially filling said member,

D. means for mechanically and electrically joining said member to saidcable conductor within said pothead, and

E. condensing means for said liquid, exterior to said insulator,communicating with said member.

2. The pothead of claim 1 wherein said joining means comprises a sleeve'extending from said member and compressible over said conductor.

3. The pothead of claim 1 comprising a downwardly 6 extending length oftubing within said member for condensate from said liquid.

4 The pothead of claim 1 wherein said condensing means comprises aplurality of radial fins and comprising a corona ring adjacent to saidfins, said ring having an outer radius at least equal to the radialextension of said fins.

5. A high-voltage termination comprising, in combination:

A. a cable comprising a conductor and a thick wall of insulationsurrounding said conductor,

B. a pothead comprising an insulator,

C. entrance means into said pothead for said cable,

said cable being surrounded by said wall of insulation,

D. an electrically conducting tubular member positioned to extendupwardly within said pothead,

E. a liquid vaporizable at the operating temperature of said pothead, atleast partially filling said member,

F. means mechanically and electrically joining said member to saidconductor within said pothead,

G. condensing means for said liquid exterior to said insulator andcommunicating with said member, and

H. wrappings within said insulator forming a continuous wall ofelectrical insulation over said conductor and said member.

6. The termination of claim 5 comprising a stress relief cone extendingupwardly over said cable, said joining means, and at least a portion ofsaid member containing said liquid.

7. The termination of claim 5 wherein said joining means comprises asleeve extending from said member and compressed over said conductor,said cable comprises temperature monitoring means and said sleevecomprises a wall defining an opening leading to said temperaturemonitoring means.

8. The termination of claim 7 comprising a radio transmitter mountedabove said condensing means for signals from said monitoring means.

9. The termination of claim 5 wherein said joining means comprises asleeve extending from said member and compressed over said conductor.

10. The termination of claim 9 wherein said cable comprises an insulatedpilot wire, said sleeve comprises a wall defining an opening for saidpilot wire and said member comprises an external lengthwise groove forsaid pilot wire, said pilot wire being positioned in said groove undersaid wrappings.

11. The termination of claim 10 comprising temperature monitoring meanssensitive to the resistance of said pilot wire, mounted above saidcondensing means.

12. The termination of claim 11 comprising a radio transmitter mountedtherewith for signals from said monitoring means.

13. The termination of claim 5 comprising temperature monitoring meansand a radio transmitter mounted above said condensing means for signalsfrom said monitoring means.

14. The method of terminating a high-voltage electric cable comprisingthe steps of:

A. exposing a substantial length of the core of said cable, includinginsulation shielding, beyond the sheath of said cable,

B. removing sufficient insulation to expose a length of the end of theconductor of said cable,

C. mechanically and electrically connecting an electrically conductingtubular member to said end,

D. wrapping insulation around said member to the member to said pothead,

diameter of the insulation on said cable, H. at least partially fillingsaid member with a liquid E. building a stress relief cone extendingfrom said vaporizable at the operating temperature of said shieldingover said core, I pothead, v F. positioning a pothead over said memberand the l. filling said pothead with dielectric fluid, and

exposed length of said core, J. sealing said pothead.

G. fitting a vapor condenser communicating with said

1. A pothead, comprising an insulator, for a high-voltage cable, saidcable comprising a conductor and a thick wall of insulation surroundingsaid conductor, comprising: A. entrance means into said pothead for saidcable having said wall of insulation, B. an electrically conductingtubular member positioned to extend upwardly within said pothead, C. aliquid vaporizable at the operating temperature of said pothead at leastpartially filling said member, D. means for mechanically andelectrically joining said member to said cable conductor within saidpothead, and E. condensing means for said liquid, exterior to saidinsulator, communicating with said member.
 2. The pothead of claim 1wherein said joining means comprises a sleeve extending from said memberand compressible over said conductor.
 3. The pothead of claim 1comprising a downwardly extending length of tubing within said memberfor condensate from said liquid.
 4. The pothead of claim 1 wherein saidcondensing means comprises a plurality of radial fins and comprising acorona ring adjacent to said fins, said ring having an outer radius atleast equal to the radial extension of said fins.
 5. A high-voltagetermination comprising, in combination: A. a cable comprising aconductor and a thick wall of insulation surrounding said conductor, B.a pothead comprising an insulator, C. entrance means into said potheadfor said cable, said cable being surrounded by said wall of insulation,D. an electrically conducting tubular member positioned to extendupwardly within said pothead, E. a liquid vaporizable at the operatingtemperature of said pothead, at least partially filling said member, F.means mechanically and electrically joining said member to saidconductor within said pothead, G. condensing means for said liquidexterior to said insulator and communicating with said member, and H.wrappings within said insulator forming a continuous wall of electricalinsulation over said conductor and said member.
 6. The termination ofclaim 5 comprising a stress relief cone extending upwardly over saidcable, said joining means, and at least a portion of said membercontaining said liquid.
 7. The termination of claim 5 wherein saidjoining means comprises a sleeve extending from said member andcompressed over said conductor, said cable comprises temperaturemonitoring means and said sleeve comprises a wall defining an openingleading to said temperature monitoring means.
 8. The termination ofclaim 7 comprising a radio transmitter mounted above said condensingmeans for signals from said monitoring means.
 9. The termination ofclaim 5 wherein said joining means comprises a sleeve extending fromsaid member and compressed over said conductor.
 10. The termination ofclaim 9 wherein said cable comprises an insulated pilot wire, saidsleeve comprises a wall defining an opening for said pilot wire and saidmember comprises an external lengthwise groove for said piloT wire, saidpilot wire being positioned in said groove under said wrappings.
 11. Thetermination of claim 10 comprising temperature monitoring meanssensitive to the resistance of said pilot wire, mounted above saidcondensing means.
 12. The termination of claim 11 comprising a radiotransmitter mounted therewith for signals from said monitoring means.13. The termination of claim 5 comprising temperature monitoring meansand a radio transmitter mounted above said condensing means for signalsfrom said monitoring means.
 14. The method of terminating a high-voltageelectric cable comprising the steps of: A. exposing a substantial lengthof the core of said cable, including insulation shielding, beyond thesheath of said cable, B. removing sufficient insulation to expose alength of the end of the conductor of said cable, C. mechanically andelectrically connecting an electrically conducting tubular member tosaid end, D. wrapping insulation around said member to the diameter ofthe insulation on said cable, E. building a stress relief cone extendingfrom said shielding over said core, F. positioning a pothead over saidmember and the exposed length of said core, G. fitting a vapor condensercommunicating with said member to said pothead, H. at least partiallyfilling said member with a liquid vaporizable at the operatingtemperature of said pothead, I. filling said pothead with dielectricfluid, and J. sealing said pothead.